Karl Jaspers was one of the architects of contemporary existentialism and one of the first philosophers to use the term existentialist. He was a prolific writer with a prolix style that is often inelegant, superficial, sentimental, and unclear and that over the years showed itself to be repetitious. Yet careful and extensive reading of his works shows him to be a rigorous and responsible thinker. Appearances notwithstanding, he was perhaps the most systematic of all existentialist philosophers. His philosophy is neither linguistic analysis nor metaphysics. It can be best characterized as a disciplined and organized description of the critical fringes of human existence, such as impenetrable limits, unmitigated freedom, and the experienced indefinite expanse of space, time, and consciousness. Jaspers fulfilled the commonsense image of the philosopher through his vital concern with the contemporary political situation and his trenchant reflections on the threats to...